TORC2 Signaling Pathway Guarantees Genome Stability in the Face of DNA Strand Breaks

• An inhibitor of yeast TORC1 and TORC2 is identified and characterized
• TORC2, but not TORC1, inhibition accentuates DNA damage induced by Zeocin
• The Ypk1/Ypk2 pathway downstream of TORC2 is implicated in this synergism
• Altered actin polymerization leads to massive chromosome fragmentation on Zeocin

SummaryA chemicogenetic screen was performed in budding yeast mutants that have a weakened replication stress response. This identified an inhibitor of target of rapamycin (TOR) complexes 1 and 2 that selectively enhances the sensitivity of sgs1Δ cells to hydroxyurea and camptothecin. More importantly, the inhibitor has strong synthetic lethality in combination with either the break-inducing antibiotic Zeocin or ionizing radiation, independent of the strain background. Lethality correlates with a rapid fragmentation of chromosomes that occurs only when TORC2, but not TORC1, is repressed. Genetic inhibition of Tor2 kinase, or its downstream effector kinases Ypk1/Ypk2, conferred similar synergistic effects in the presence of Zeocin. Given that Ypk1/Ypk2 controls the actin cytoskeleton, we tested the effects of actin modulators latrunculin A and jasplakinolide. These phenocopy TORC2 inhibition on Zeocin, although modulation of calcineurin-sensitive transcription does not. These results implicate TORC2-mediated actin filament regulation in the survival of low levels of DNA damage.